With the increasing importance of electric mobility, issues of rotor cooling in electrical machines are increasingly taking on relevance. This is especially true for machines with high power density, such as are used in the automobile industry as driving motors. It has already been proposed, in order to take heat away from the rotor, to provide a hollow shaft into which a cooling agent is introduced by means of a lance. Due to centrifugal force during the movement of the rotor, the cooling agent flows along the hollow shaft. The drawback is that seals for taking in and/or discharging the cooling agent must withstand high mechanical stresses and therefore need to have a very sophisticated design and are prone to malfunction. Furthermore, considerable frictional losses occur at the seal.
In order to avoid the cooling of the rotor via its shaft, it has already been proposed to outfit the rotor with one or a plurality of cooling ducts, through which the cooling agent flows. For this, the cooling agent may be introduced into an annular space of the rotor, which is joined communicating with the cooling duct or one particular cooling duct. The cooling agent collecting in the annular space is conveyed axially through the cooling duct or ducts by centrifugal force during the movement of the rotor.
DE 11 2008 000 535 T5 discloses a cooling structure for rotary electrical machines in which magnetic uptake holes are provided in a rotor core such that they extend between axial end faces of the core, and cavities are provided each time in contact with permanent magnets so as to extend between the end faces of the core. Moreover, a feed duct for rotor cooling fluid is provided for feeding cooling fluid to a core end face, wherein the cooling fluid fed from the rotor cooling fluid feed duct is introduced into the cavities. A ring-shaped reservoir region is provided on a holder on the rotor side.
However, the integration of an annular space in a holder of the rotor requires a complex design of the holder, which significantly increases the manufacturing expense of such a rotor.
JP 2002 345 188 A discloses a rotor, in which permanent magnets are secured in magnet insert holes which are formed in a rotor core and which extend along a rotor shaft. Along the magnet insert holes are cooling ducts that carry a cooling fluid along the magnet insert holes and are formed such that their cross section protrudes toward the center of rotation.
TW 2014 21870 A discloses an oil-cooled motor, comprising a housing, a stator and a rotor, which has a rotor cooling duct. The volume between the stator and the rotor forms a cylindrical oil duct. By circulation of a cooling agent inside the motor, the heat generated by the motor is discharged.